The present invention relates to a sheet finishing apparatus for stapling recording sheets, on which an image is recorded by an image forming apparatus, by a stapler and for delivering the stapled sheets outside the image forming apparatus. Specifically, the present invention relates to a sheet alignment means, provided in a sheet finishing apparatus, which can satisfy high speed processing.
A sheet finishing apparatus, which is called a finisher, is used as an apparatus in which a plurality of sheets, on which images have been recorded, and which are delivered outside the image forming apparatus, are collated and stapled by a stapling means for each copy volume.
In this finisher, its functions are combined with an image forming apparatus main body, and are driven corresponding to sequence operations of the copying process.
Accordingly, a finisher is required in which high speed processing can be carried out, matching the speed of an image forming apparatus in which high speed copy processing can be carried out.
Proposals for such a finisher, by which high speed processing can be carried out, are disclosed in the following publications: Japanese Patent Publication Open to Public Inspection Nos. 142359/1985, 158463/1985, 239169/1987, 288002/1987, 267667/1988, and 276691/1990, and Japanese Patent Publication No. 41991/1993.
In the sheet finishing apparatus, the following operations are carried out. A sheet, on which the image has been recorded, and which has been delivered from an image forming apparatus, is aligned in an intermediate stacker and successively placed on the stacker. After one copy set of sheets have been placed on the stacker, sheet finishing processing such as stapling are carried out. A volume of stapled sheets is sent by a transfer lever of a sheet transfer means, and conveyed by a delivering belt provided at the bottom of the intermediate stacker. The volume of sheets are sandwiched by a pair of sheet delivery rollers, which are vertically provided, and delivered on a sheet delivery tray.
As a conventional sheet finishing processing apparatus, provided with this kind of stapler, an apparatus, in which a movable member for sheet width regulation is operated, is disclosed in Japanese Patent Publication Open to Public Inspection No. 288003/1987, or the like. Further, a sheet alignment apparatus of an intermediate sheet feed apparatus in a two-sided copier is disclosed in Japanese Patent Publication No. 15391/1994.
Sheets, which are conveyed from the image forming apparatus to the sheet finishing processing apparatus, and which are sent to the stacker after the sheets have been conveyed by the conveyance rollers, are delivered dispersively in the direction of sheet width. Accordingly, movable alignment plates of an alignment means are largely withdrawn in the direction of the sheet width when sheets are conveyed into the stacker. In the sheets, the first sheet slides on the stacker surface and contacts with a stopper, and is aligned in the sheet advancing direction. The succeeding sheets slide on the first sheet and advance to the stopper position. A rotational delivery belt, located such that it slightly protrudes from the stacker surface, delivers a stapled sheet volume outside the image forming apparatus. Since the first sheet, which slides on the stacker, slides directly on the delivery belt, the first sheet does not easily slip down in the direction of the stopper, so that a time lag is caused by the first sheet. Accordingly, the time until the first sheet arrives the stop position, is longer than that in the case of other sheets. Further, sheet skewing tends to occur. Accordingly, when normal sheet-alignment is carried out during the above-described period, the movable alignment plates press the side edges of sheets, and the sheet is prevented from advancing, resulting in non-uniform sheet alignment in the sheet advance direction.
Next, before the alignment operation by the movable alignment plates, the movable alignment plates are in a waiting position in which the plates are wide opened (for example, the sheet width+20 mm). The movable alignment plates receive sheets and are moved for sheet alignment in the direction of sheet advance in this status. However, when the sheet alignment operation is carried out under the conditions described above, it is necessary that the movable alignment plates are moved quite a bit from the waiting position to the sheet side edges. Accordingly, sheets are moved excessively, so that unacceptable alignment tends to occur.
Since sheets are laterally pushed during sheet slip-down by the alignment operation of the movable alignment plates, the sheets are aligned at an angle with respect to the rotating direction of the auxiliary conveyance member or the auxiliary conveyance belt, which are arranged at the sheet alignment reference side. Accordingly, a sheet having large curl on its end is caught in the above-described member, in which case unacceptable alignment occurs.